The present invention relates to the polymerization of ethylene in the presence of catalysts known in the art as Ziegler catalysts.
Ziegler catalysts are commonly formed by reducing a transition metal compound with an organometallic compound. The reduced transition metal compound is then used, alone or in conjunction with an activator, which may be the same or a different organometallic compound, to polymerize olefins, especially ethylene, in the presence of an inert solvent. A molecular weight regulator, such as hydrogen, may be used with these catalyst systems, as taught by Vandenberg in U.S. Pat. No. 3,051,690.
Ziegler et al, in U.S. Pat. No. 3,070,549 teach that catalysts can be prepared by reduction of transition metal salts with organometallic compounds of magnesium or zinc, either alone or in combination with organoaluminum compounds. Yields in the order of 500 grams of polyethylene per gram of transition metal were obtained.
Ziegler et al, in U.S. Pat. No. 3,392,162 teach that the organometallic compound used as reducing agent for the transition metal salts can be mixed complexes of organolithium and organoaluminum, organomagnesium or organozinc compounds. Similar low yields of polyethylene were obtained.
We have previously shown, in copending application Ser. No. 722,794, filed Feb. 2, 1977 that catalysts prepared by reduction of tetrabutyl titanate with a mixed magnesium-aluminum alkyl followed by deactivation of any excess magnesium alkyl by the addition of hydrogen chloride gave extremely high yields of polyethylene when this catalyst was used in combination with a trialkylaluminum activator-scavenger to polymerize ethylene in an inert hydrocarbon solvent at low pressures. Unfortunately, in the absence of the activator-scavenger during the polymerization, only a trace amount of polymer was formed using the same catalyst.